Conventionally, in an electronic device such as a cellular telephone that is configured by connecting two bodies, a technique is known, in which a light emitting/receiving unit (a light emitting unit and a light receiving unit) is provided in a first body, a plurality of reflecting portions each having a different reflection efficiency are provided, and the levels of the light reflected on the reflecting portions are detected, thereby detecting a relative rotation position between the two bodies (for example, see Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-235722